New efficient representation of photographic images with restricted number of gray levels

Variations of existing methods are presented to produce high quality representations of black and white photographic images even when only a very restricted number of gray levels can be used on the available displays in printers. The cost-effective methods are based on error diffusion and Hilbert curver traversal. Solutions are given to certain slight problems that arise when the basic idea is applied in too straightforward a manner. Images printed on a laser printer have an extraordinarily close resemblance to real photographs, and even eight gray levels seems to be sufficient for displaying crisp images. The results indicate that two pixels could well be stored in each byte, reducing the required space by half for images meant for display purposes only